A comparison of the availability and ileal digestibility of lysine in cottonseed and soya-bean meals for grower/finisher pigs.

The availability of lysine and the ileal digestibility of amino acids in three cottonseed meals and a soya-bean meal for grower/finisher pigs were determined. The usefulness of the availability estimates for formulating diets was assessed. The availability of lysine, as assessed with a slope-ratio assay, was (proportion of total): cottonseed meal no. 1, 0.27; no. 2, 0.30; no. 3, 0.29; soya-bean meal, 0.90. Ileal digestibility of lysine in the meals (proportion of total) was: cottonseed meal no. 1, 0.58; no. 2, 0.68; no. 3, 0.72; soya-bean meal, 0.89. Pigs given diets formulated to the same available lysine concentration grew at similar rates and retained the same amount of lysine in the carcasses. The results indicate that, for meals of high availability (soya-bean meal), reduced ileal digestibility appears to be the main reason for reduced availability. However, in meals of low availability (cottonseed meal), reduced ileal digestibility only accounts for part of the reduced availability. Thus, the ileal digestibility of lysine is not a reliable indicator of lysine availability.